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TPL7407L: TPL7407 broken randomly

user5837177
Prodigy 40 points
Part Number: TPL7407L

Hi, 

We are using TPL7407 in order to drive 6 solenoid valves which have 24V operating voltage and approximately 250 mA current rating per valve. The valve driver circuit has been designed as advised in its datasheet, I added reverse schottky diode to OUT7 (which is actually unused) and Ccom capacitance with 100V voltage rating. All digital inputs are coming via optocouplers to preserve microcontroller side, and there is a resettable fuse, 1000 mA trip current, to avoid excessive current usage on COM power line. Our problem is that it sometimes breaks suddenly, you can see its photo below. I am being suspicious of loose contact between solenoid valves and the circuit, and it creates sudden current peaks but I guess it should be handled in solenoid driver IC. Do you have any suggestions about it?

  • 0
    TI__Genius 10652 points

    Hi,

    Can you please share with me your schematic?

    And what is the operating conditions where you see failure? All solenoids on ?

    Best

    Dimitri

  • 0 in reply to dimitri james
    Prodigy 40 points

    Hi, 

    Thank you for your interest. You can see the schematic below. valveCOM net is 24V and its current is limited via 1000 mA resettable fuse. While we have 6 solenoid valves, only two of them are operating at the same time.The failure occurs generally while valve1 and valve5 are open at the same time. A spike occurs and there is a hole on the IC as you can see in the previous photo. I have experienced this situation 3-4 times up to now.

  • 0 in reply to user5837177
    TI__Genius 10652 points

    Hi,

    Thank you for sharing schematic. When exactly does the failure event occur? Is it during turn-on of the solenoidds Valv1/5, steady state, or turn-off.

    Because of the nature of the inductive load, it can create positive, or negative spike in response to the turn-on/off event which can damage the device for larger inductive load.

    If you can share any waveforms of Valve1_out, Valve5_out, and control signal just before the failure event it could help us diagnose which part of operation caused the failrue.


    Also, do you have any flyback diodes for each channel? i am not seeing any in your schematic. They are important to protect against inductive overshoot on OUTX. If you have them, please share the shematic with them and please tell the p/n.

    Best

    Dimitri

  • 0 in reply to dimitri james
    Prodigy 40 points

    Hi,

    The failure generally occurs while solenoid valves are moving from OFF to ON.

    It is the whole schematic for solenoid valve driver in our circuit, so there is no additional flyback diodes because TPL7407 includes them. Do we need to use extra flyback diodes and why?

    Thank you.

  • 0 in reply to user5837177
    TI__Genius 10652 points

    Internal diode inside TPL7407L are not necessarily sufficient, relying on them can inject a lot of current during transitions on output due to inductive spikes.

    Please try implement flyback diodes on each channel. This can go from output to valveCOM

    Secondly, since you mentioned that the issue occurs when going from OFF to ON, can you try to add schottky from GND to channel like you have on Channel 7.

    The purpose of this diode is to clamp negative spike below ground

    Inductive load can cause negative spikes BELOW GND or ABOVE valveCOM, which can damage the device by current injection, which is why i recommend to try adding flyback / schottky clamp for protection first since you shared it seemed the issue is happening on transistions on output.

    You can also try switch to TPL7407LA which is a revised version of this IC and a little more robust.

    Can you try addingthe flyback / schottky clamps

    Best

    Dimitri